Rigging a ball type character for a game
I don't know if this is playable in unity, but I'll give it a shot anyways.

I would recommend using basic keyboard controls for the main movement, and mouse-look for both the cannons and the head.

Here are the settings for the body movement.


Also, if you want the head to stay with the body, parent it to the body, and the cannons to the head.

Here are the settings for rotating the head.


If the head's rotation isn't working, click on the "Use X axis" button and click on the "Use Y axis" to disable the incorrect rotation.

Use the same settings for the cannons, but inverted (Click on the "Use X/Y axis" until the settings are opposite of the head settings).